The study aim is to determine the effects of fluoride on the growth and metabolism of cariogenic Streptococcus mutans. The goals of the current year were to screen five potential mechanisms of NaF inhibition in strains differing in fluoride sensitivity: 1) growth; 2) viability; 3) metabolism; 4) adherence; and 5) fluoride adaptation/mutation. The bacteriocidal action of fluoride (600 ppm) for fluoride-sensitive and fluoride-resistant strains was temperature and pH dependent. The antimetabolic actions of fluoride were assessed by: 1) carbohydrate fermentation patterns; 2) substrate utilization and endproduct synthesis; 3) intracellular polysaccharide (IPS) and enzyme production; and, 4) glucose uptake. Fluoride effects on adherence were studied by comparing gross plaque accumulation on extracted teeth exposed to 5% sucrose fluoride-free cultures of FS and FR strains. Fluoride therapy can generate S. mutans strains that adapt to fluoride and demonstrate a phenotypic expression of fluoride resistance that is rapidly lost in the absence of fluoride. The present findings indicate that fluoride may affect S. mutans in ways dependent on fluoride concentration, age of cell, natural or induced fluoride sensitivity and nature of the environment.